I need batteries to power my arudino bass cat for a minimum of a couple of hours at a time. Been reading lots of threads about using AA or 9v and which is more power efficient. People are saying AA is better… what do you guys think? It would have to power an arduino with about 2 capacitive sensors and an Adafruit waveshield with about a 3" speaker, I might add an extra amp and larger speaker to the configuration if need be.

This article lists the sizes, shapes, and general characteristics of some common primary and secondary battery types in household and light industrial use. Historically the term "battery" referred to a collection of electrochemical cells connected in series, however in modern times the term has come to refer to any collection of cells (or single cell) packaged in a container with external connections provided to power electrical devices, leading to the variety of standardized form factors availab...

AA batteries will offer a longer lifecycle but in terms of efficientcy thats all relative, is 6 AAs better than 1 9v? I think a rechargable lithium Ion battery like Chris suggested is honestly the best route but if your looking for standard batteries it really depends on the amount of space you are ok with your battery pack taking up and the overall amperage you need over time. If we assume an average of 200 milliamps drawn then an average 9V would net you about 2.5-3 hours.